John Gill Commentary Ezekiel 31:4

"The waters nourished it, the deep made it to grow: the rivers thereof ran round about its plantation; and it sent out its channels unto all the trees of the field." — Ezekiel 31:4 (ASV)

The waters made him great

The waters of the river Tigris, near to which stood the city of Nineveh, the metropolis of the Assyrian monarchy; the traffic brought by which river made it rich and great, and the whole empire, and the king of it.

the deep set him up on high, with her rivers running round about his plants

The vast trade by sea, the profits and commodities of which were conveyed through various rivers, which ran about the provinces of the empire, which were as plants in a field; and by which they were enriched, and the whole empire, and the king of it, were raised to a prodigious pitch of wealth and power.

and sent out little rivers to all the trees of the field

So that the common people, comparable to the trees of the field for their number and usefulness, all received profit and advantage hereby.

Or else by waters and the deep may be meant the multitude of people, as in (Revelation 17:15), which increased his kingdom, filled his provinces, supplied his colonies, and enlarged his power and riches.

The Targum is, "by the people he was multiplied; by his auxiliaries he became strong; he subjected kings under his government; and his governors he appointed over all the provinces of the earth."